The present invention refers to a cartridge assembly, comprising a cartridge having a rigid cartridge cylinder, a membrane containing liquid chemical and having a closed end and an outlet end disposed in said cartridge, and a piston assembly, arranged thus, that the membrane is turned outside-in within itself by the action of the piston such that the inner surfaces of the turned outside in wall portions of the membrane slide relative to each other during emptying of the package.
The use of a thin wall plastic film or plastic film/metal foil laminate membrane sausage shaped package to contain and to dispense a chemical such as an adhesive or sealant is well known. The membrane package is placed within a cartridge type container which acts as a mechanical support while the membrane is scraped off the cartridge wall and compacted to expel its content, the cartridge type container being re-usable. Despite the advantage of a considerably reduced package structure for disposal, this above mentioned principle of compacting the package requires a much greater dispensing force in relation to a conventional cartridge due to the force required for scraping off and progressively compacting the foil package from the supporting inner cartridge wall while the package is under significant hydraulic pressure. This issue of force is very important especially for manually actuated dispensing devices where only a limited hand force is available.
As an alternative to the above, European Patent Application No. 369,723 discloses a similar package but with the difference that the membrane is turned outside-in by a plunger, rather than being scraped off the wall under pressure and compacted, which considerably increases the relative mechanical efficiency.
However, this prior art according to the introduction of the independent claims, acknowledges that a leak path of the package content will exist between the two adjacent membrane walls and also that the leak path will be smaller or greater depending upon the clearance between the plunger and the cartridge cylinder internal diameter which determines the gap between the two adjacent membrane walls. Therefore, dependant upon viscosity of the liquid chemical content, the pressure being applied in order to dispense the content and the size of leak path, the effect can be to discharge part of the content of the membrane rearwards past the plunger instead of ahead of the plunger and out of the package, thus disturbing the ratio and increasing waste. This rearwards discharge is the result of leak between the two package membranes adjacent to the plunger and into the trailing membrane package behind the plunger where it will inflate, and may burst, the membrane under pressure.